1. Field of the Invention
The present invention relates to a body-insertable apparatus and an in-vivo acquisition system.
2. Description of the Related Art
Conventionally, there are body-insertable apparatuses that are perorally inserted into a subject, such as a living body, and acquire in-vivo images of the subject. In such a body-insertable apparatus, for example, an illumination unit, an image sensor, and a transmission circuit that transmits acquired images by radio to a receiving device, which is arranged outside the subject, are housed in a capsule-shaped casing. A body-insertable apparatus including such an imaging means is conventionally configured to correct the value of optical black (OB) in an acquired image, i.e., to perform a black level correction (hereinafter, “OB correction”) in the apparatus (see Japanese Laid-open Patent publication No. 2006-140642).
For example, an image sensor with which a body-insertable apparatus is equipped with acquires an image of an object that is illuminated with illumination light from an illumination unit. After signal processing, such as correlated double sampling, is performed on an analog image signal that is output from the image sensor, the analog image signal is converted by an A/D converter to a digital signal. After digital signal processing, such as OB correction and offset adjustment, are performed on the digitized image signal, the image signal is sent to a transmission circuit and then transmitted from the transmission circuit to the outside of the subject via an antenna. The OB correction can be performed by simply dividing a digital signal by an offset or by performing a feedback process on the analog signal.
The body-insertable apparatus is also equipped with a light adjustment circuit that adjusts the amount of light of the illumination unit. The light adjustment circuit performs a light measurement process on an image signal obtained by an image sensor. In the light measurement process, the brightness of a target image is obtained using a simple average, weighting average, and peak value of luminance of a predetermined region, or using a value calculated from combinations thereof. In addition, the brightness of a target image can be obtained using the signal level of each pixel. The image signal to be processed may be an analog signal or a digital signal.
The light adjustment circuit adjusts the amount of light (the amount of light emission or light emission time) of the illumination unit for capturing of an image of the next frame according to the result obtained by the light measurement process. For example, when the result obtained by the light measurement process does not reach a pre-set target value, the light adjustment circuit increases the amount of light of the illumination unit for capturing of an image of the next frame. In contrast, when the result obtained by the light measurement process exceeds the pre-set target value, the light adjustment circuit reduces the amount of light of the illumination unit for capturing of an image of the next frame. By adjusting the amount of light of the illumination unit for capturing of an image of the next frame according to the brightness of the image of the next frame as described above, an image in which approximately equal brightness is maintained can be acquired even if, for example, the distance between the body-insertable apparatus and the object varies.